(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method and structure for the creation of A Metal Oxide Semiconductor tunneling Light Emitter Diode and CMOS devices over the surface of one semiconductor substrate.
(2) Description of the Prior Art
In the creation of semiconductor devices, it is frequently advantageous to create functionally different devices over the surface of one substrate, whereby in addition the process of creating the devices of different functionality is partially or in totality combined. In order to achieve this latter objective, the processes of creating functionally different devices over the surface of one substrate must be compatible processes and must further be extended to comprise interconnecting the created devices in order to create one unit comprising diverse and functionally cooperative devices. As one of the significant advantages that can be achieved using this approach is the always present and importance consideration of cost effectiveness.
Complementary Metal Oxide Semiconductor (CMOS) devices take up a significant portion of presently used semiconductor devices. By combining the CMOS device with a MOS tunneling Light Emitter Diode (LED) diode capability, it is now possible to create over the surface of one semiconductor device a device that can be applied for the creation of small-scale or micro images. This combined capability requires the creation of junctions that interface between surface regions created over the surface of a substrate of different conductivity, such as a junction between a region of n-type conductivity and an underlying well of p-type conductivity (referred to as an N#+/PW junction) or a junction between an n-well that is created over the surface of a substrate having p-type conductivity (referred to as an NW/Psub junction). These junctions have in the art been widely used as detectors that form a functional part of a Light Detecting Diode. Recent advantages in realizing low-voltage operation of CMOS devices have led to the development of MOS LED devices. It has thereby been observed that as advantageous factors in the design of such MOS LED devices can be applied decreasing the thickness of a layer of gate oxide of the gate electrode, as this layer becomes part of the LED (Light Emitter Diode) function, and of increasing the roughness of the oxide layer that is used for the creation of a MOS LED, which can lead to enhanced light emission of the MOS LED. The latter aspect of increasing surface roughness has been proposed to be achieved by creating the layer of gate oxide using methods of low-temperature oxidation, which result in increasing oxide layer surface roughness. This however also results in reducing the quality of the layer of gate oxide underneath the gate electrode, which has a severely negative impact on gate electrode performance and which is therefore unacceptable as a design approach. It is therefore of advantage to use a dual gate oxide process, combined with the application of a gate oxide dry etch, which combined methods allow for the creation of MOS LED devices. The invention provides such a method.
U.S. Pat. No. 6,1242,324 B1 (Kub et al.) shows a process for LED devices over CMOS devices.
U.S. Pat. No. 6,346,445 B1 (Hsu) shows a dual gate oxide process.
U.S. Pat. No. 6,335,262 B1 (Crowder et al.) shows another dual gate oxide process.
U.S. Pat. No. 5,1994,204 (Young et al.) shows a LED process with light shields.
A principle objective of the invention is to simultaneously create CMOS devices and MOS tunneling Light Emitting Diodes over the surface of one semiconductor substrate.
Another objective of the invention is to provide a method for creating ultra-thin layer of gate oxide while as part of the same processing stream creating a layer of oxide of desired surface roughness.
In accordance with the objectives of the invention a new method is provided for the combined creation of CMOS devices and MOS tunneling LED devices. The process starts with a semiconductor substrate over the surface of which are designated a first surface region for the creation of CMOS devices there over and a second surface region for the creation of MOS tunneling LED devices there over. A relatively thick layer of gate oxide is created over the surface of the substrate. The first surface region is blocked by a mask of photoresist after which the second surface region is exposed to a plasma etch, thereby providing roughness to the surface of the relatively thin layer of gate oxide. The blocking mask is removed, additional oxidation of the exposed surface creates a relatively thick layer of gate oxide over the first surface area and a relatively thin layer of gate oxide over the second surface area.